Revert "net: sit: fix memory leak in sit_init_net()"

This reverts commit 375d6d45 which is
commit 07f12b26 upstream.

Unnecessarily calling free_netdev() from sit_init_net().
ipip6_dev_free() of 4.9.y called free_netdev(), so no need
to call again after ipip6_dev_free().

Cc: Mao Wenan <maowenan@huawei.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Ajay Kaher <akaher@vmware.com>
Reviewed-by: Mao Wenan <maowenan@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

net/ipv6/sit.c

@@ -1856,7 +1856,6 @@ static int __net_init sit_init_net(struct net *net)
 
 err_reg_dev:
 	ipip6_dev_free(sitn->fb_tunnel_dev);
-	free_netdev(sitn->fb_tunnel_dev);
 err_alloc_dev:
 	return err;
 }